Replace the three images in system/library/coreservices/springboardapp which are 
AwayBulletinListCellSeparatorDark@2x.png 
AwayBulletinListCellSeparatorLight@2x.png 
BulletinListCellSeparator@2x.png 
by the transparent 2x4 pixels png-files.
Rename the originals by putting a 1 in front of the filename.

many thanks to Benjammin123